在Flutter中使用shared_preferences在设备上本地保存对象列表

Question

我创建了一个可以发送红外信号的应用程序，你可以自己添加红外信号。这些信号被保存在一个名为Item的对象列表中，以Item为对象。我想要的名称和信号本地保存在设备上的应用程序运行，但项目从未保存:以下是代码:

import 'package:flutter/material.dart';
import 'package:ir_sensor_plugin/ir_sensor_plugin.dart';
import 'package:flutter/services.dart';
import 'package:shared_preferences/shared_preferences.dart';
import 'dart:async';
import 'dart:convert';
class Item {
String buttonName = "", hexCode = "";
bool isSelected = false;
Item({
required this.buttonName,
required this.hexCode,
});
// Method to convert the Item object to a JSON object
Map<String, dynamic> toJson() {
return {
'buttonName': buttonName,
'hexCode': hexCode,
'isSelected': isSelected,
};
}
// Method to convert a JSON object to an Item object
static Item fromJson(Map<String, dynamic> json) {
return Item(
buttonName: json['buttonName'],
hexCode: json['hexCode'],
);
}
}
class IrRemoteEmulator extends StatefulWidget {
const IrRemoteEmulator({Key? key}) : super(key: key);
@override
State<IrRemoteEmulator> createState() => _IrRemoteEmulatorState();
}
class _IrRemoteEmulatorState extends State<IrRemoteEmulator> {
String buttonName = "";
TextEditingController _buttonName = TextEditingController();
String hexCode = "";
TextEditingController _hexCode = TextEditingController();
List<Item> items = [
Item(
buttonName: "Samsung Power",
hexCode:
"0000 006d 0022 0003 00a9 00a8 0015 003f 0015 003f 0015 003f 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 003f 0015 003f 0015 003f 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 003f 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0040 0015 0015 0015 003f 0015 003f 0015 003f 0015 003f 0015 003f 0015 003f 0015 0702 00a9 00a8 0015 0015 0015 0e6e"),
Item(
buttonName: "Prowise Power",
hexCode:
"0000 006d 0022 0003 00a9 00a8 0015 003f 0015 003f 0015 003f 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 003f 0015 003f 0015 003f 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 003f 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0040 0015 0015 0015 003f 0015 003f 0015 003f 0015 003f 0015 003f 0015 003f 0015 0702 00a9 00a8 0015 0015 0015 0e6e")
];
// Method to save the items list to the local storage
Future<void> saveList(List<Item> items) async {
// Get the instance of the shared preferences
final prefs = await SharedPreferences.getInstance();
// Convert the items list to a JSON string
var itemsJson = json.encode(items);
// Save the JSON string to the local storage
prefs.setString('items', itemsJson);
debugPrint("Items saved");
}
Future<List<Item>> loadList() async {
// Get the instance of the shared preferences
final prefs = await SharedPreferences.getInstance();
// Retrieve the JSON string from the local storage
var itemsJson = prefs.getString('items') ?? '';
// Convert the JSON string to a List<Item> object
var items = json.decode(itemsJson);
debugPrint("Items loaded");
return items;
}
String selectedHexcode =
"0000 006d 0022 0003 00a9 00a8 0015 003f 0015 003f 0015 003f 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 003f 0015 003f 0015 003f 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 003f 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0040 0015 0015 0015 003f 0015 003f 0015 003f 0015 003f 0015 003f 0015 003f 0015 0702 00a9 00a8 0015 0015 0015 0e6e";
String _platformVersion = 'Unkown';
bool _hasIrEmitter = false;
String _getCarrierFrequencies = 'Unknown';
@override
void initState() {
super.initState();
// Load the saved items list from the local storage
loadList().then((savedItems) {
// Set the items list to the loaded list
setState(() {
items = savedItems;
});
});
initPlatformState();
}
// Platform messages are asynchronous, so we initialize in an async method.
Future<void> initPlatformState() async {
String platformVersion;
bool hasIrEmitter;
String getCarrierFrequencies;
// Platform messages may fail, so we use a try/catch PlatformException.
try {
platformVersion = await IrSensorPlugin.platformVersion;
hasIrEmitter = await IrSensorPlugin.hasIrEmitter;
getCarrierFrequencies = await IrSensorPlugin.getCarrierFrequencies;
} on PlatformException {
platformVersion = 'Failed to get data in a platform.';
hasIrEmitter = false;
getCarrierFrequencies = 'None';
}
// If the widget was removed from the tree while the asynchronous platform
// message was in flight, we want to discard the reply rather than calling
// setState to update our non-existent appearance.
if (!mounted) return;
setState(() {
_platformVersion = platformVersion;
_hasIrEmitter = hasIrEmitter;
_getCarrierFrequencies = getCarrierFrequencies;
});
}
@override
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner: false,
home: Scaffold(
body: Center(
child: Column(
children: [
const SizedBox(
height: 25,
),
const SizedBox(
height: 15.0,
),
Container(
decoration:
BoxDecoration(border: Border.all(color: Colors.white)),
child: Padding(
padding: const EdgeInsets.all(8.0),
child: Column(
children: [
FloatingActionButton.large(
onPressed: () async {
final String result =
await IrSensorPlugin.transmitString(
pattern: selectedHexcode);
debugPrint('Emitting  List Int Signal: $result');
},
child: const Icon(Icons.power_settings_new_outlined),
),
],
),
),
),
Expanded(
child: SizedBox(
height: 200,
child: ListView.builder(
itemCount: items.length,
itemBuilder: (context, index) {
return ListTile(
onTap: () {
items[index].isSelected = true;
selectedHexcode = items[index].hexCode;
debugPrint(items[index].hexCode);
setState(() {});
},
onLongPress: () {
items.remove(items[index]);
saveList(items);
setState(() {});
},
title: Text(items[index].buttonName),
leading: Icon((items[index].hexCode == selectedHexcode)
? Icons.circle
: Icons.circle_outlined),
);
},
),
),
),
],
),
),
floatingActionButton: FloatingActionButton.extended(
onPressed: () => showDialog(
context: context,
builder: (context) => AlertDialog(
title: const Text("Add IR Hexcode"),
content: Column(
children: <Widget>[
TextFormField(
controller: _buttonName,
decoration: InputDecoration(
labelText: "Remotebutton name",
hintText: "Ac Powerbutton",
hintStyle: TextStyle(color: Colors.grey[300])),
),
TextFormField(
controller: _hexCode,
decoration: InputDecoration(
labelText: "Hexcode",
hintText:
"0000 006d 0022 0003 00a9 00a8 0015 003f 0015 003f 0015 003f 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 003f 0015 003f 0015 003f 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 003f 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0015 0040 0015 0015 0015 003f 0015 003f 0015 003f 0015 003f 0015 003f 0015 003f 0015 0702 00a9 00a8 0015 0015 0015 0e6e",
hintStyle: TextStyle(color: Colors.grey[300])),
),
],
),
actions: [
TextButton(
child: const Text("Cancel"),
onPressed: () => Navigator.pop(context),
),
TextButton(
child: const Text("Ok"),
onPressed: () {
if (_hexCode.text.isEmpty || _buttonName.text.isEmpty) {
debugPrint("${(items.length)}");
} else {
items.add(Item(
buttonName: _buttonName.text,
hexCode: _hexCode.text,
));
saveList(items);
debugPrint("${(items)}");
}
Navigator.pop(context);
setState(() {});
return;
},
),
],
),
),
label: const Text("Add IR Hexcode"),
icon: const Icon(Icons.add),
),
),
);
}
}

我尝试添加Shared_preferences，但是当我添加了一个新信号并重新打开应用程序时，整个应用程序被重置，我看不到新添加的信号。有人能帮我吗?

Answer 1

In

Future<void> saveList(List<Item> items) async {
// Get the instance of the shared preferences
final prefs = await SharedPreferences.getInstance();
// Convert the items list to a JSON string
var itemsJson = json.encode(items);
// Save the JSON string to the local storage
prefs.setString('items', itemsJson);
debugPrint("Items saved");
}

您不是在保存项，而是在更新项(因为setString替换了SharedPreferences中按键存储的所有数据)。SharedPreferences不是存储用户数据的好解决方案(因为它们是为存储偏好而设计的，它不是数据库)。出于您的目的，您需要使用数据库。如果数据量不大，可以使用hive.